Metal Oxide Ceramic and Method of Making Articles Therewith

ABSTRACT

Disclosed herein is a ceramic comprising: at least two different metal oxides, the at least two different metal oxides comprising TiO 2  and La 2 O 3  or TiO 2  and BaO; less than 20% by weight SiO 2 ; less than 20% by weight B 2 O 3 ; and less than 40% by weight P 2 O 5 ; the ceramic having a glass transition temperature, T g , and a crystallization onset temperature, T x , and the difference between T g  and T x  is at least 5K. The ceramic may comprise additional metal oxides. Also disclosed herein is a method of making an article using the ceramic; typically, the ceramic is heated above the T g , shaped, and then cooled.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 10/211,491, filedAug. 2, 2002, which is a continuation-in-part of U.S. Ser. No.09/922,526, filed Aug. 2, 2001, now abandoned, the disclosures of whichare incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a metal oxide ceramic and a method ofmaking articles therewith. Examples of articles include kitchenware(e.g., plates), dental brackets, and reinforcing fibers, cutting toolinserts, abrasives, and structural components of gas engines, (e.g.,valves and bearings).

DESCRIPTION OF RELATED ART

A large number of glass and glass-ceramic compositions are known. Themajority of oxide glass systems utilize well-known glass-formers such asSiO₂, B₂O₃, P₂O₅, GeO₂, TeO₂, As₂O₃, and V₂O₅ to aid in the formation ofthe glass. Some of the glass compositions formed with theseglass-formers can be heat-treated to form glass-ceramics. The upper usetemperature of glasses and glass-ceramics formed from such glass formersis generally less than 1200° C., typically about 700-800° C. Theglass-ceramics tend to be more temperature resistant than the glass fromwhich they are formed.

Although a large number of metal oxides can be obtained in an amorphousstate by melting and rapidly quenching, most, because of the need forvery high quench rates to provide amorphous rather than crystallinematerial, cannot be formed into bulk or complex shapes. Generally, suchsystems are very unstable against crystallization during subsequentreheating and therefore do not exhibit typical properties of glass suchas viscous flow. On the other hand, glasses based on the known networkforming oxides (e.g., SiO₂ and B₂O₃) are generally relatively stableagainst crystallization during reheating and, correspondingly, the“working” range where viscous flow occurs can be readily accessed.Formation of large articles from powders of known glass (e.g., SiO₂ andB₂O₃) via viscous sintering at temperatures above glass transitiontemperature is well known. For example, in the abrasive industry,grinding wheels are made using vitrified bond to secure the abrasiveparticles together.

It is desirable to provide large articles and/or complex shapescomprising non-traditional glass and glass-ceramic compositions.

SUMMARY OF THE INVENTION

Disclosed herein is a ceramic comprising: at least two different metaloxides, the at least two different metal oxides comprising TiO₂ andLa₂O₃ or TiO₂ and BaO; less than 20% by weight SiO₂; less than 20% byweight B₂O₃; and less than 40% by weight P₂O₅; the ceramic having aglass transition temperature, T_(g), and a crystallization onsettemperature, T_(x), and the difference between T_(g) and T_(x) is atleast 5K. The ceramic may also comprise an additional metal oxideselected from the group consisting of Al₂O₃, CaO, Cr₂O₃, CoO, Fe₂O₃,GeO₂, HfO₂, Li₂O, MgO, MnO, NiO, Na₂O, P₂O₅, CeO₂, Dy₂O₃, Er₂O₃, Eu₂O₃,Gd₂O₃, Ho₂O₃, Lu₂O₃, Nd₂O₃, Pr₆O₁₁, Sm₂O₃, Th₄O₇, Tm₂O₃, Yb₂O₃, Sc₂O₃,SiO₂, SrO, TeO₂, TiO₂, V₂O₃, Y₂O₃, ZnO, ZrO₂, and combinations thereof.

Also disclosed herein is a method of making an article, comprising:providing a glass in a form comprising particles, beads, microspheres,or fibers; the glass comprising: at least two different metal oxides,the at least two different metal oxides comprising TiO₂ and La₂O₃ orTiO₂ and BaO; less than 20% by weight SiO₂; less than 20% by weightB₂O₃; and less than 40% by weight P₂O₅; the glass having a glasstransition temperature, T_(g), and a crystallization onset temperature,T_(x), and the difference between T_(g) and T_(x) is at least 5K; andheating the glass above the T_(g) to coalesce to form a coalesced shape;and cooling the coalesced shape.

The method may further comprise providing a substrate including an outersurface; wherein heating the glass above the T_(g) comprises heating theglass such that at least a portion of the glass wets at least a portionof the outer surface; and wherein after cooling, the coalesced shape isattached to the outer surface.

The glass used in the disclosed method may further comprise a secondglass having a second glass transition temperature, T_(g2), and a secondcrystallization onset temperature, T_(x2), and the difference betweenT_(g2) and T_(x2) is at least 5K.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a DTA curve of Example 1 material; and

FIGS. 2-6 are DTA curves of Examples 2, 5, 6, 7, and 9 materials,respectively.

DETAILED DESCRIPTION

The present invention provides a method of making articles from glass.Optionally, the articles may be a composite of two or more differentglass compositions or formulations. In some embodiments the glass isoptionally heat-treated to at least partially crystallize the glass.

One embodiment of the present invention provides a method of making anarticle from glass comprising:

-   -   providing a substrate (e.g., ceramics, metals, intermetallics,        and composites thereof) including an outer surface;    -   providing at least a first glass (e.g., sheets, particles        (including microspheres), and fibers), wherein the first glass        comprises at least two different metal oxides (i.e., the metal        oxides do not have the same cation(s)), wherein the first glass        has a T_(g) and T_(x), and wherein the difference between the        T_(g) and the T_(x) of the first glass is at least 5K (or even,        at least 10K, at least 15K, at least 20K, at least 25K, at least        30K, or at least 35K), the first glass containing less than 20%        by weight SiO₂ (or even less than 15%, less than 10%, less than        5% by weight, or even zero percent, by weight, SiO₂), less than        20% by weight B₂O₃ (or even less than 15%, less than 10%, less        than 5% by weight, or even zero percent, by weight, B₂O₃), and        less than 40% by weight P₂O₅ (or even less than 35%, less than        30%, less than 25%, less than 20%, less than 15%, less than 10%,        less than 5% by weight, or even zero percent, by weight, P₂O₅);    -   heating the first glass above the T_(g) such that at least a        portion of the glass wets at least a portion of the outer        surface of the substrate; and    -   cooling the glass to provide an article comprising ceramic        comprising the glass attached to the at least a portion of the        outer surface of the substrate. In some embodiments, the ceramic        is glass. Optionally, the method can be practiced with a second,        a third, or more, different glass, including glasses having,        respectively, a T_(g) and T_(x), and wherein the difference        between each T_(g) and the T_(x) of a glass is at least 5K (or        even, at least 10K, at least 15K, at least 20K, at least 25K, at        least 30K,or at least 35K), one or more of the additional        glasses optionally contain less than 20% by weight SiO₂ (or even        less than 15%, less than 10%, less than 5% by weight, or even        zero percent, by weight, SiO₂), less than 20% by weight B₂O₃ (or        even less than 15%, less than 10%, less than 5% by weight, or        even zero percent, by weight, B₂O₃), and less than 40% by weight        P₂O₅ (or even less than 35%, less than 30%, less than 25%, less        than 20%, less than 15%, less than 10%, less than 5% by weight,        or even zero percent, by weight, P₂O₅). Preferably the glass, or        if more than one glass is used, at least one of the glasses,        comprises less than 40 percent (preferably, less than 35, 30,        25, 20, 15, 10, 5, or even 0) by weight glass collectively SiO₂,        B₂O₃, and P₂O₅, based on the total weight of the glass.

Another embodiment of the present invention provides a method of makingan article from glass comprising:

-   -   providing a substrate including an outer surface;    -   providing at least a first plurality of particles comprising        glass (including glass particles), wherein the glass comprises        at least two different metal oxides, wherein the glass has a        T_(g) and T_(x), and wherein the difference between the T_(g)        and the T_(x) of the glass is at least 5K (or even, at least        10K, at least 15K, at least 20K, at least 25K, at least 30K, or        at least 35K), the glass containing less than 20% by weight SiO₂        (or even less than 15%, less than 10%, less than 5% by weight,        or even zero percent, by weight, SiO₂), less than 20% by weight        B₂O₃ (or even less than 15%, less than 10%, less than 5% by        weight, or even zero percent, by weight, B₂O₃), and less than        40% by weight P₂O₅ (or even less than 35%, less than 30%, less        than 25%, less than 20%, less than 15%, less than 10%, less than        5% by weight, or even zero percent, by weight, P₂O₅);    -   heating the glass above the T_(g) such that at least a portion        of the glass of the first plurality of particles wets at least a        portion of the outer surface of the substrate; and    -   cooling the glass to provide an article comprising ceramic        comprising the glass attached to the at least a portion of the        outer surface of the substrate. In some embodiments, the ceramic        is glass. Optionally, the method can be practiced with a second,        a third, or more, different pluralities of particles comprising        (different) glasses, including glasses having, respectively, a        T_(g) and T_(x), and wherein the difference between each T_(g)        and the T_(x) of a glass is at least 5K (or even, at least 10K,        at least 15K, at least 20K, at least 25K, at least 30K, or at        least 35K), one or more of the additional glasses optionally        contain less than 20% by weight SiO₂ (or even less than 15%,        less than 10%, less than 5% by weight, or even zero percent, by        weight, SiO₂), less than 20% by weight B₂O₃ (or even less than        15%, less than 10%, less than 5% by weight, or even zero        percent, by weight, B₂O₃), and less than 40% by weight P₂O₅ (or        even less than 35%, less than 30%, less than 25%, less than 20%,        less than 15%, less than 10%, less than 5% by weight, or even        zero percent, by weight, P₂O₅). Preferably the glass, or if more        than one glass is used, at least one of the glasses, comprises        less than 40 (preferably, less than 35, 30, 25, 20, 15, 10, 5,        or even 0) percent by weight glass collectively SiO₂, B₂O₃, and        P₂O₅, based on the total weight of the glass.

Another embodiment of the present invention provides a method of makingan article comprising:

-   -   providing at least a first glass and second glass (e.g., sheets,        particles (including microspheres), and fibers), wherein the        first glass comprises at least two different metal oxides,        wherein the first glass has a T_(g1) and T_(x1), and wherein the        difference between the T_(g1) and the T_(x1) is at least 5K (or        even, at least 10K, at least 15K, at least 20K, at least 25K, at        least 30K, or at least 35K), the first glass containing less        than 20% by weight SiO₂ (or even less than 15%, less than 10%,        less than 5% by weight, or even zero percent, by weight, SiO₂),        less than 20% by weight B₂O₃ (or even less than 15%, less than        10%, less than 5% by weight, or even zero percent, by weight,        B₂O₃), and less than 40% by weight P₂O₅ (or even less than 35%,        less than 30%, less than 25%, less than 20%, less than 15%, less        than 10%, less than 5% by weight, or even zero percent, by        weight, P₂O₅);    -   heating the first and second glasses above at least T_(g1) and        at least the first glass coalescing with the second glass to        provide the article. Optionally, the second glass has a T_(g2)        and T_(x2), wherein the difference between T_(g2) and T_(x2) is        at least 5K (or even, at least 10K, at least 15K, at least 20K,        at least 25K, at least 30K, or at least 35K). Optionally, the        second glass contains less than 20% by weight SiO₂ (or even less        than 15%, less than 10%, less than 5% by weight, or even zero        percent, by weight, SiO₂), less than 20% by weight B₂O₃ (or even        less than 15%, less than 10%, less than 5% by weight, or even        zero percent, by weight, B₂O₃), and less than 40% by weight P₂O₅        (or even less than 35%, less than 30%, less than 25%, less than        20%, less than 15%, less than 10%, less than 5% by weight, or        even zero percent, by weight, P₂O₅). Optionally, the method can        be practiced with a third, a fourth, glass, etc. including        glasses having, respectively, a T_(g) and T_(x), and wherein the        difference between each T_(g) and the T_(x) of a glass is at        least 5K (or even, at least 10K, at least 15K, at least 20K, at        least 25K, at least 30K, or at least 35K), one or more of the        additional glasses optionally contain less than 20% by weight        SiO₂ (or even less than 15%, less than 10%, less than 5% by        weight, or even zero percent, by weight, SiO₂), less than 20% by        weight B₂O₃ (or even less than 15%, less than 10%, less than 5%        by weight, or even zero percent, by weight, B₂O₃), and less than        40% by weight P₂O₅ (or even less than 35%, less than 30%, less        than 25%, less than 20%, less than 15%, less than 10%, less than        5% by weight, or even zero percent, by weight, P₂O₅). The        glasses may have the same composition, different composition, or        combinations thereof. Preferably at least one of the glasses        comprise less than 40 (preferably, less than 35, 30, 25, 20, 15,        10, 5,or even 0) percent by weight glass collectively SiO₂,        B₂O₃, and P₂O₅, based on the total weight of the glass.

Another embodiment of the present invention provides a method of makingan article comprising:

-   -   providing at least a first glass and second glass (e.g., sheets,        particles (including microspheres), and fibers), wherein the        first glass comprises at least two different metal oxides,        wherein the first glass has a T_(g1) and T_(x1), and wherein the        difference between the T_(g1) and the T_(x1) is at least 5K (or        even, at least 10K, at least 15K, at least 20K, at least 25K, at        least 30K, or at least 35K), the first glass containing less        than 20% by weight SiO₂ (or even less than 15%, less than 10%,        less than 5% by weight, or even zero percent, by weight, SiO₂),        less than 20% by weight B₂O₃ (or even less than 15%, less than        10%, less than 5% by weight, or even zero percent, by weight,        B₂O₃), and less than 40% by weight P₂O₅ (or even less than 35%,        less than 30%, less than 25%, less than 20%, less than 15%, less        than 10%, less than 5% by weight, or even zero percent, by        weight, P₂O₅), and wherein the second glass comprises at least        two different metal oxides, wherein the second glass has a        T_(g2) and T_(x2), and wherein the difference between the T_(g2)        and the T_(x2) is at least 5K (or even, at least 10K, at least        15K, at least 20K, at least 25K, at least 30K, or at least 35K),        the second glass containing less than 20% by weight SiO₂ (or        even less than 15%, less than 10%, less than 5% by weight, or        even zero percent, by weight, SiO₂), less than 20% by weight        B₂O₃ (or even less than 15%, less than 10%, less than 5% by        weight, or even zero percent, by weight, B₂O₃), and less than        40% by weight P₂O₅ (or even less than 35%, less than 30%, less        than 25%, less than 20%, less than 15%, less than 10%, less than        5% by weight, or even zero percent, by weight, P₂O₅);    -   heating the glasses above the higher of T_(g1) or T_(g2) and        coalescing the first and second glasses to provide the article.        Optionally, the method can be practices with a third, a fourth,        glass, etc. including glasses having, respectively, a T_(g) and        T_(x), and wherein the difference between each T_(g) and the Tx        of a glass is at least 5K (or even, at least 10K, at least 15K,        at least 20K, at least 25K, at least 30K, or at least 35K), one        or more of the additional glasses optionally contain less than        20% by weight SiO₂ (or even less than 15%, less than 10%, less        than 5% by weight, or even zero percent, by weight, SiO₂), less        than 20% by weight B₂O₃ (or even less than 15%, less than 10%,        less than 5% by weight, or even zero percent, by weight, B₂O₃),        and less than 40% by weight P₂O₅ (or even less than 35%, less        than 30%, less than 25%, less than 20%, less than 15%, less than        10%, less than 5% by weight, or even zero percent, by weight, P₂        _(O5)). The glasses may have the same composition, different        composition, or combinations thereof Preferably at least one of        the glasses comprise less than 40 (preferably, less than 35, 30,        25, 20, 15, 10, 5, or even 0) percent by weight glass        collectively SiO₂, B₂O₃, and P₂O₅, based on the total weight of        the glass.

Another embodiment of the present invention provides a method of makingan article comprising:

-   -   providing at least a first plurality of particles comprising        glass (including glass particles), wherein the glass comprises        at least two different metal oxides, wherein the glass has a        T_(g) and T_(x), and wherein the difference between the T_(g)        and the T_(x) of the glass is at least 5K (or even, at least        10K, at least 15K, at least 20K, at least 25K, at least 30K, or        at least 35K), the glass containing less than 20% by weight SiO₂        (or even less than 15%, less than 10%, less than 5% by weight,        or even zero percent, by weight, SiO₂), less than 20% by weight        B₂O₃ (or even less than 15%, less than 10%, less than 5% by        weight, or even zero percent, by weight, B₂O₃), and less than        40% by weight P₂O₅ (or even less than 35%, less than 30%, less        than 25%, less than 20%, less than 15%, less than 10%, less than        5% by weight, or even zero percent, by weight, P₂O₅);    -   heating the glass above the T_(g) and coalescing at least a        portion of the first plurality of particles to provide the        article. In some embodiments, the ceramic is glass. Optionally,        the method can be practiced with a second, a third, or more,        different pluralities of particles comprising (different)        glasses, including glasses having, respectively, a T_(g) and        T_(x), and wherein the difference between each T_(g) and the        T_(x) of a glass is at least 5K (or even, at least 10K, at least        15K, at least 20K, at least 25K, at least 30K, or at least 35K),        one or more of the additional glasses optionally contain less        than 20% by weight SiO₂ (or even less than 15%, less than 10%,        less than 5% by weight, or even zero percent, by weight, SiO₂),        less than 20% by weight B₂O₃ (or even less than 15%, less than        10%, less than 5% by weight, or even zero percent, by weight,        B₂O₃), and less than 40% by weight P₂O₅ (or even less than 35%,        less than 30%, less than 25%, less than 20%, less than 15%, less        than 10%, less than 5% by weight, or even zero percent, by        weight, P₂O₅). Preferably the glass, or if more than one glass        is used, at least one of the glasses, comprises less than 40        (preferably, less than 35, 30, 25, 20, 15, 10, 5, or even 0)        percent by weight glass collectively SiO₂, B₂O₃, and P₂O₅, based        on the total weight of the glass.

Desirably, the ratio of a T_(g) to T₁ is at least 0.5. Examples ofuseful glass particles include those comprising REO-Al₂O₃—ZrO₂ andREO-Al₂O₃—ZrO₂—SiO₂ glasses. Other useful glasses may also includeCaO—Al₂O₃, CaO—Al₂O₃—ZrO₂, BaO—TiO₂, La₂O₃—TiO₂, REO (i.e., rare earthoxide(s))-Al₂O₃ glasses.

Embodiments of the method according to the present invention, includingfor certain ceramic compositions, allow for the formation of articleshapes and sizes that were obtainable from conventional methods.Coalescence of the glass is typically enhanced if the glass is underpressure during heating. In one embodiment, a charge of glass (e.g.,particles (including beads), fibers, etc. is placed into a die andhot-pressing is performed at temperatures above glass transition whereviscous flow of glass leads to coalescence into an article.

In this application:

“amorphous material” refers to material derived from a melt and/or avapor phase that lacks any long range crystal structure as determined byX-ray diffraction and/or has an exothermic peak corresponding to thecrystallization of the amorphous material as determined by a DTA(differential thermal analysis) as determined by the test describedherein entitled “Differential Thermal Analysis”;

“ceramic” includes amorphous material, glass, crystalline ceramic,glass-ceramic, and combinations thereof,

“glass” refers to amorphous material exhibiting a glass transitiontemperature;

“glass-ceramic” refers to ceramic comprising crystals formed byheat-treating amorphous material;

“rare earth oxides” refers to cerium oxide (e.g.,CeO₂), dysprosium oxide(e.g., Dy₂O₃), erbium oxide (e.g., Er₂O₃), europium oxide (e.g., Eu₂O₃),gadolinium (e.g., Gd₂O₃), holmium oxide (e.g., Ho₂O₃), lanthanum oxide(e.g., La₂O₃), lutetium oxide (e.g., Lu₂O₃), neodymium oxide (e.g.,Nd₂O₃), praseodymium oxide (e.g., Pr₆O₁₁), samarium oxide (e.g., Sm₂O₃),terbium (e.g., Tb₂O₃), thorium oxide (e.g., Th₄O₇), thulium (e.g.,Tm₂O₃), and ytterbium oxide (e.g., Yb₂O₃), and combinations thereof,

“REO” refers to rare earth oxide(s);

“T_(g)” refers to the glass transition temperature as determined inExample 1;

“T₁” refers to the glass melting point; and

“T_(x)” refers to crystallization onset temperature as determined inExample 1.

Further, it is understood herein that unless it is stated that a metaloxide (e.g., Al₂O₃, complex Al₂O₃ metal oxide, etc.) is crystalline, forexample, in a glass-ceramic, it may be amorphous, crystalline, orportions amorphous and portions crystalline. For example if aglass-ceramic comprises Al₂O₃ and ZrO₂, the Al₂O₃ and ZrO₂ may each bein an amorphous state, crystalline state, or portions in an amorphousstate and portions in a crystalline state, or even as a reaction productwith another metal oxide(s) (e.g., unless it is stated that, forexample, Al₂O₃ is present as crystalline Al₂O₃ or a specific crystallinephase of Al₂O₃ (e.g alpha Al₂O₃), it may be present as crystalline Al₂O₃and/or as part of one or more crystalline complex Al₂O₃.metal oxides.Further, it is understood that glass-ceramics formed by heatingamorphous material not exhibiting a T_(g) may not actually compriseglass, but rather may comprise the crystals and amorphous material thatdoes not exhibiting a T_(g).

Optionally certain glass articles made according to the presentinvention can be heat-treated at least partially crystallize the glassto provide glass-ceramic.

In general, ceramics according to the present invention can be made byheating (including in a flame) the appropriate metal oxide sources toform a melt, desirably a homogenous melt, and then rapidly cooling themelt to provide amorphous materials or ceramic comprising amorphousmaterials. Amorphous materials and ceramics comprising amorphousmaterials according to the present invention can be made, for example,by heating (including in a flame) the appropriate metal oxide sources toform a melt, desirably a homogenous melt, and then rapidly cooling themelt to provide amorphous material. Embodiments of amorphous materialscan be made, for example, by melting the metal oxide sources in anysuitable furnace (e.g., an inductive heated furnace, a gas-firedfurnace, or an electrical furnace), or, for example, in a plasma. Theresulting melt is cooled (e.g., discharging the melt into a coolingmedia (e.g., high velocity air jets, liquids, metal plates (includingchilled metal plates), metal rolls (including chilled metal rolls),metal balls (including chilled metal balls), and the like)).

Embodiments of amorphous materials can also be obtained by othertechniques, such as: laser spin melt with free fall cooling, Taylor wiretechnique, plasmatron technique, hammer and anvil technique, centrifugalquenching, air gun splat cooling, single roller and twin rollerquenching, roller-plate quenching and pendant drop melt extraction (see,e.g., Rapid Solidification of Ceramics, Brockway et. al, Metals AndCeramics Information Center, A Department of Defense InformationAnalysis Center, Columbus, Ohio, January, 1984, the disclosure of whichis incorporated here as a reference). Embodiments of amorphous materialsmay also be obtained by other techniques, such as: thermal (includingflame or laser or plasma-assisted) pyrolysis of suitable precursors,physical vapor synthesis (PVS) of metal precursors and mechanochemicalprocessing.

In one method, glass useful for the present invention can be madeutilizing flame fusion as disclosed, for example, in U.S. Pat. No.6,254,981 (Castle), the disclosure of which is incorporated herein byreference. In this method, the metal oxide sources materials are fed(e.g., in the form of particles, sometimes referred to as “feedparticles”) directly into a burner (e.g., a methane-air burner, anacetylene-oxygen burner, a hydrogen-oxygen burner, and like), and thenquenched, for example, in water, cooling oil, air, or the like. Feedparticles can be formed, for example, by grinding, agglomerating (e.g.,spray-drying), melting, or sintering the metal oxide sources. The sizeof feed particles fed into the flame generally determines the size ofthe resulting glass particles/beads.

Examples of useful glass for carrying out the present invention includethose comprising CaO—Al₂O₃, CaO—Al₂O₃—ZrO₂, BaO—TiO₂, La₂O₃—TiO₂,REO-Al₂O₃, REO-Al₂O₃—ZrO₂, REO-Al₂O₃—ZrO₂—SiO₂, and SrO—Al₂O₃—ZrO₂glasses. Useful glass formulations include those at or near a eutecticcomposition. In addition to the CaO—Al₂O₃, CaO—Al₂O₃—ZrO₂, BaO—TiO₂,La₂O₃—TiO₂, REO-Al₂O₃, REO-Al₂O₃—ZrO₂, REO-Al₂O₃—ZrO_(2—SiO) ₂, andSrO—Al₂O₃—ZrO₂ compositions disclosed herein, other compositions,including eutectic compositions, will be apparent to those skilled inthe art after reviewing the present disclosure. For example, phasediagrams depicting various compositions, including eutecticcompositions, are known in the art.

Surprisingly, it was found that ceramics of present invention could beobtained without limitations in dimensions. This was found to bepossible through a coalescence step performed at temperatures aboveglass transition temperature. For instance, as evident from FIG. 1,glass useful in carry out the present invention undergoes glasstransition (T_(g)) before significant crystallization occurs (T_(x)) asevidenced by the existence of endotherm (T_(g)) at lower temperaturethan exotherm (T_(x)). This allows for bulk fabrication of articles ofany dimensions from relatively small pieces of glass. More specifically,for example, an article according to the present invention, can beprovided by heating, for example, glass particles (including beads andmicrospheres), fibers, etc. useful in carrying out the present inventionabove the T_(g) such that the glass particles, etc. coalesce to form ashape and cooling the coalesced shape to provide the article. In certainembodiments, heating is conducted at at least one temperature in a rangeof about 725° C. to about 1100° C.

Surprisingly, for certain embodiments according to the presentinvention, coalescence may be conducted at temperatures significantlyhigher than crystallization temperature (T_(x)). Although not wanting tobe bound by theory, it s is believed the relatively slow kinetics ofcrystallization allow access to higher temperatures for viscous flow.Typically, the glass is under pressure during coalescence to aid thecoalescence of the glass. In one embodiment, a charge of the glassparticles, etc. is placed into a die and hot-pressing is performed attemperatures above glass transition where viscous flow of glass leads tocoalescence into a relatively large part. Typically, the amorphousmaterial is under pressure (e.g., greater than zero to 1 GPa or more)during coalescence to aid the coalescence of the amorphous material. Itis also within the scope of the present invention to conduct additionalcoalescence to further improve desirable properties of the article. Forexample, hot-isostatic pressing may be conducted (e.g., at temperaturesfrom about 900° C. to about 1400° C.) to remove residual porosity,increasing the density of the material. It is also within the scope ofthe present invention to coalesce glass via hot-isostatic pressing, hotextrusion, or other pressure assisted techniques.

Heat-treatment can be carried out in any of a variety of ways, includingthose known in the art for heat-treating glass to provideglass-ceramics. For example, heat-treatment can be conducted in batches,for example, using resistive, inductively or gas heated furnaces.Alternatively, for example, heat-treatment can be conductedcontinuously, for example, using rotary kilns. In the case of a rotarykiln, the material is fed directly into a kiln operating at the elevatedtemperature. The time at the elevated temperature may range from a fewseconds (in some embodiments even less than 5 seconds) to a few minutesto several hours. The temperature may range anywhere from 900° C. to1600° C., typically between 1200° C. to 1500° C. It is also within thescope of the present invention to perform some of the heat-treatment inbatches (e.g., for the nucleation step) and another continuously (e.g.,for the crystal growth step and to achieve the desired density). For thenucleation step, the temperature typically ranges between about 900° C.to about 1100° C., in some embodiments, preferably in a range from about925° C. to about 1050° C. Likewise for the density step, the temperaturetypically is in a range from about 1100° C. to about 1600° C., in someembodiments, preferably in a range from about 1200° C. to about 1500° C.This heat treatment may occur, for example, by feeding the materialdirectly into a furnace at the elevated temperature. Alternatively, forexample, the material may be feed into a furnace at a much lowertemperature (e.g., room temperature) and then heated to desiredtemperature at a predetermined heating rate. It is within the scope ofthe present invention to conduct heat-treatment in an atmosphere otherthan air. In some cases it might be even desirable to heat-treat in areducing atmosphere(s). Also, for, example, it may be desirable toheat-treat under gas pressure as in, for example, hot-isostatic press,or in gas pressure furnace.

Sources, including commercial sources, of metal oxides such as Al₂O₃,BaO, CaO, rare earth oxides (e.g., CeO₂, Dy₂O₃, Er₂O₃, Eu₂O₃, Gd₂O₃,Ho₂O₃, La₂O₃, Lu₂O₃, Nd₂O₃, Pr₆O₁₁, Sm₂O₃, Th₄O₇, Tm₂O₃, and Yb₂O₃, andcombinations thereof), TiO₂, ZrO₂ are known in the art. For examplesources of (on a theoretical oxide basis) Al₂O₃ include bauxite(including both natural occurring bauxite and synthetically producedbauxite), calcined bauxite, hydrated aluminas (e.g., boehmite, andgibbsite), aluminum, Bayer process alumina, aluminum ore, gamma alumina,alpha alumina, aluminum salts, aluminum nitrates, and combinationsthereof. The Al₂O₃ source may contain, or only provide, Al₂O₃.Alternatively, the Al₂O₃ source may contain, or provide Al₂O₃, as wellas one or more metal oxides other than Al₂O₃ (including materials of orcontaining complex Al₂O₃ metal oxides (e.g., Dy₃Al₅O₁₂, Y₃Al₅O₁₂,CeAl₁₁O₁₈, etc.).

Sources, including commercial sources, of rare earth oxides include rareearth oxide powders, rare earth metals, rare earth-containing ores(e.g., bastnasite and monazite), rare earth salts, rare earth nitrates,and rare earth carbonates. The rare earth oxide(s) source may contain,or only provide, rare earth oxide(s). Alternatively, the rare earthoxide(s) source may contain, or provide rare earth oxide(s), as well asone or more metal oxides other than rare earth oxide(s) (includingmaterials of or containing complex rare earth oxides (e.g., Dy₃Al₅O₁₂,CeAl₁₁O₁₈, etc.).

Sources, including commercial sources, of (on a theoretical oxide basis)ZrO₂ include zirconium oxide powders, zircon sand, zirconium,zirconium-containing ores, and zirconium salts (e.g., zirconiumcarbonates, acetates, nitrates, chlorides, hydroxides, and combinationsthereof). In addition, or alternatively, the ZrO₂ source may contain, orprovide ZrO₂, as well as other metal oxides such as hafnia. Sources,including commercial sources, of (on a theoretical oxide basis) HfO₂include hafnium oxide powders, hafnium, hafnium-containing ores, andhafnium salts. In addition, or alternatively, the HfO₂ source maycontain, or provide HfO₂, as well as other metal oxides such as ZrO₂.

Sources, including commercial sources, of BaO include barium oxidepowders, barium-containing ores, barium salts, barium nitrates, andbarium carbonates. The barium oxide source may contain, or only provide,barium oxide. Alternatively, the barium oxide source may contain, orprovide barium oxide, as well as one or more metal oxides other thanbarium oxide (including materials of or containing complex bariumoxide).

Sources, including commercial sources, of CaO include calcium oxidepowders and calcium-containing ores. The calcium oxide(s) source maycontain, or only provide, calcium oxide. Alternatively, the calciumoxide source may contain, or provide calcium oxide, as well as one ormore metal oxides other than calcium oxide (including materials of orcontaining complex calcium oxide).

Sources, including commercial sources, of rare earth oxides include rareearth oxide powders, rare earth metals, rare earth-containing ores(e.g., bastnasite and monazite), rare earth salts, rare earth nitrates,and rare earth carbonates. The rare earth oxide(s) source may contain,or only provide, rare earth oxide(s). Alternatively, the rare earthoxide(s) source may contain, or provide rare earth oxide(s), as well asone or more metal oxides other than rare earth oxide(s) (includingmaterials of or containing complex rare earth oxides (e.g., Dy₃Al₅O₁₂,CeAl₁₁O₁₈, etc.).

Sources, including commercial sources, of SiO₂ include silica powders,silicon metals, silicon-containing ores. The silicon oxide source maycontain, or only provide, silicon oxide. Alternatively, the siliconoxide source may contain, or provide silicon oxide, as well as one ormore metal oxides other than silicon oxide (including materials of orcontaining complex silicon oxide).

Sources, including commercial sources, of SrO include strontium oxidepowders, strontium carbonates, and strontium-containing ores. Thestrontium oxide source may contain, or only provide, strontium oxide.Alternatively, the strontium oxide source may contain, or providestrontium oxide, as well as one or more metal oxides other thanstrontium oxide (including materials of or containing complex strontiumoxide).

Sources, including commercial sources, of TiO₂ include titanium oxidepowders, titanium metals and titanium-containing ores. The titaniumoxide source may contain, or only provide, titanium oxide.Alternatively, the titanium oxide source may contain, or providetitanium oxide, as well as one or more metal oxides other than titaniumoxide (including materials of or containing complex titanium oxide).

Sources, including commercial sources, of (on a theoretical oxide basis)ZrO₂ include zirconium oxide powders, zircon sand, zirconium,zirconium-containing ores, and zirconium salts (e.g., zirconiumcarbonates, acetates, nitrates, chlorides, hydroxides, and combinationsthereof). In addition, or alternatively, the ZrO₂ source may contain, orprovide ZrO₂, as well as other metal oxides such as hafnia. Sources,including commercial sources, of (on a theoretical oxide basis) HfO₂include hafnium oxide powders, hafnium, hafnium-containing ores, andhafnium salts. In addition, or alternatively, the HfO₂ source maycontain, or provide HfO₂, as well as other metal oxides such as ZrO₂.

Optionally, ceramics according to the present invention further compriseadditional metal oxides beyond those needed for the general composition.The addition of certain metal oxides may alter the properties and/or thecrystalline structure or microstructure of ceramics made according tothe present invention, as well as the processing of the raw materialsand intermediates in making the ceramic. For example, oxide additionssuch as MgO, CaO, Li₂O, and Na₂O have been observed to alter both theT_(g) and T_(x) of glass. Although not wishing to be bound by theory, itis believed that such additions influence glass formation. Further, forexample, such oxide additions may decrease the melting temperature ofthe overall system (i.e., drive the system toward lower meltingeutectic), and ease of glass-formation. Complex eutectics in multicomponent systems (quaternary, etc.) may result in better glass-formingability. The viscosity of the liquid melt and viscosity of the glass inits' “working” range may also be affected by the addition of metaloxides beyond those needed for the general composition.

In some instances, it may be preferred to incorporate limited amounts ofmetal oxides selected from the group consisting of: Na₂O, P₂O₅, SiO₂,TeO₂, V₂O₃, and combinations thereof. Sources, including commercialsources, include the oxides themselves, complex oxides, ores,carbonates, acetates, nitrates, chlorides, hydroxides, etc. These metaloxides may be added, for example, to modify a physical property of theresulting abrasive particles and/or improve processing. These metaloxides when used are typically are added from greater than 0 to 20% byweight, preferably greater than 0 to 5% by weight and more preferablygreater than 0 to 2% by weight of the glass-ceramic depending, forexample, upon the desired property.

Further other glass compositions which may be used in conjunction withthe required glass(es) for carrying out the present invention includethose conventional glasses that are well known in the art, includingsources thereof.

For glasses that devitrify to form glass-ceramics, crystallization mayalso be affected by the additions of materials beyond those needed forthe general composition. For example, certain metals, metal oxides(e.g., titanates and zirconates), and fluorides, for example, may act asnucleation agents resulting in beneficial heterogeneous nucleation ofcrystals. Also, addition of some oxides may change nature of metastablephases devitrifying from the glass upon reheating. In another aspect,for ceramics according to the present invention comprising crystallineZrO₂, it may be desirable to add metal oxides (e.g., Y₂O₃, TiO₂, CaO,and MgO) that are known to stabilize tetragonal/cubic form of ZrO₂.

Examples of optional metal oxides (i.e., metal oxides beyond thoseneeded for the general composition) may include, on a theoretical oxidebasis, Al₂O₃, BaO, CaO, Cr₂O₃, CoO, Fe₂O₃, GeO₂, HfO₂, Li₂O, MgO, MnO,NiO, Na₂O, P₂O₅, rare earth oxides, Sc₂O₃, SiO₂, SrO, TeO₂, TiO₂, V₂O₃,Y₂O₃, ZnO, ZrO₂, and combinations thereof. Sources, including commercialsources, include the oxides themselves, complex oxides, ores,carbonates, acetates, nitrates, chlorides, hydroxides, etc. Further, forexample, with regard to Y₂O₃, sources, including commercial sources, of(on a theoretical oxide basis) Y₂O₃ include yttrium oxide powders,yttrium, yttrium-containing ores, and yttrium salts (e.g., yttriumcarbonates, nitrates, chlorides, hydroxides, and combinations thereof).The Y₂O₃ source may contain, or only provide, Y₂O₃. Alternatively, theY₂O₃ source may contain, or provide Y₂O₃, as well as one or more metaloxides other than Y₂O₃ (including materials of or containing complexY₂O₃ (e.g., Y₃Al₅O₁₂).

In some embodiments, it may be advantageous for at least a portion of ametal oxide source (in some embodiments, preferably, 10 15, 20, 25, 30,35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or even at least 95percent by weight) to be obtained by adding particulate, metallicmaterial comprising at least one of a metal (e.g., Al, Ca, Cu, Cr, Fe,Li, Mg, Ni, Ag, Ti, Zr, and combinations thereof), M, that has anegative enthalpy of oxide formation or an alloy thereof to the melt, orotherwise metal them with the other raw materials. Although not wantingto be bound by theory, it is believed that the heat resulting from theexothermic reaction associated with the oxidation of the metal isbeneficial in the formation of a homogeneous melt and resultingamorphous material. For example, it is believed that the additional heatgenerated by the oxidation reaction within the raw material eliminatesor minimizes insufficient heat transfer, and hence facilitates formationand homogeneity of the melt, particularly when forming amorphousparticles with x, y, and z dimensions over 150 micrometers. It is alsobelieved that the availability of the additional heat aids in drivingvarious chemical reactions and physical processes (e.g., densification,and spherodization) to completion. Further, it is believed for someembodiments, the presence of the additional heat generated by theoxidation reaction actually enables the formation of a melt, whichotherwise is difficult or otherwise not practical due to high meltingpoint of the materials. Further, the presence of the additional heatgenerated by the oxidation reaction actually enables the formation ofamorphous material that otherwise could not be made, or could not bemade in the desired size range. Another advantage of the inventioninclude, in forming the amorphous materials, that many of the chemicaland physical processes such as melting, densification and spherodizingcan be achieved in a short time, so that very high quench rates be canachieved. For additional details, see copending application having U.S.Ser. No. 10/211639, filed the same date as the instant application, thedisclosure of which is incorporated herein by reference.

The particular selection of metal oxide sources and other additives formaking ceramics according to the present invention typically takes intoaccount, for example, the desired composition and microstructure of theresulting ceramics, the desired degree of crystallinity, if any, thedesired physical properties (e.g., hardness or toughness) of theresulting ceramics, avoiding or minimizing the presence of undesirableimpurities, the desired characteristics of the resulting ceramics,and/or the particular process (including equipment and any purificationof the raw materials before and/or during fusion and/or solidification)being used to prepare the ceramics.

The metal oxide sources and other additives can be in any form suitableto the process and equipment utilized for the present invention. The rawmaterials can be melted and quenched using techniques and equipmentknown in the art for making oxide glasses and amorphous metals.Desirable cooling rates include those of 50 K/s and greater. Coolingtechniques known in the art include roll-chilling. Roll-chilling can becarried out, for example, by melting the metal oxide sources at atemperature typically 20-200° C. higher than the melting point, andcooling/quenching the melt by spraying it under high pressure (e.g.,using a gas such as air, argon, nitrogen or the like) onto a high-speedrotary roll(s). Typically, the rolls are made of metal and are watercooled. Metal book molds may also be useful for cooling/quenching themelt.

Other techniques for forming melts, cooling/quenching melts, and/orotherwise forming glass include vapor phase quenching, plasma spraying,melt-extraction, and gas atomization. Vapor phase quenching can becarried out, for example, by sputtering, wherein the metal alloys ormetal oxide sources are formed into a sputtering target(s) which areused. The target is fixed at a predetermined position in a sputteringapparatus, and a substrate(s) to be coated is placed at a positionopposing the target(s). Typical pressures of 10⁻³ torr of oxygen gas andAr gas, discharge is generated between the target(s) and a substrate(s),and Ar or oxygen ions collide against the target to start reactionsputtering, thereby depositing a film of composition on the substrate.For additional details regarding plasma spraying, see, for example,copending application having U.S. Ser. No. 10/211640, filed the samedate as the instant application, the disclosure of which is incorporatedherein by reference.

Gas atomization involves melting feed particles to convert them to melt.A thin stream of such melt is atomized through contact with a disruptiveair jet (i.e., the stream is divided into fine droplets). The resultingsubstantially discrete, generally ellipsoidal glass particles are thenrecovered. Melt-extraction can be carried out, for example, as disclosedin U.S. Pat. No. 5,605,870 (Strom-Olsen et al.), the disclosure of whichis incorporated herein by reference. Containerless glass formingtechniques utilizing laser beam heating as disclosed, for example, inPCT application having Publication No. WO 01/27046 A1, published Apr. 4,2001, the disclosure of which is incorporated herein by reference, mayalso be useful in making glass according to the present invention.

The cooling rate is believed to affect the properties of the quenchedamorphous material. For instance, glass transition temperature, densityand other properties of glass typically change with cooling rates.

Rapid cooling may also be conducted under controlled atmospheres, suchas a reducing, neutral, or oxidizing environment to maintain and/orinfluence the desired oxidation states, etc. during cooling. Theatmosphere can also influence glass formation by influencingcrystallization kinetics from undercooled liquid. For example, largerundercooling of Al₂O₃ melts without crystallization has been reported inargon atmosphere as compared to that in air.

With regard to making particles, for example, the resulting ceramic(e.g., glass or ceramic comprising glass may be larger in size than thatdesired. The ceramic can be, and typically is, converted into smallerpieces using crushing and/or comminuting techniques known in the art,including roll crushing, canary milling, jaw crushing, hammer milling,ball milling, jet milling, impact crushing, and the like. In someinstances, it is desired to have two or multiple crushing steps. Forexample, after the ceramic is formed (solidified), it may be in the formlarger than desired. The first crushing step may involve crushing theserelatively large masses or “chunks” to form smaller pieces. Thiscrushing of these chunks may be accomplished with a hammer mill, impactcrusher or jaw crusher. These smaller pieces may then be subsequentlycrushed to produce the desired particle size distribution. In order toproduce the desired particle size distribution (sometimes referred to asgrit size or grade), it may be necessary to perform multiple crushingsteps. In general the crushing conditions are optimized to achieve thedesired particle shape(s) and particle size distribution.

The shape of particles can depend, for example, on the composition ofthe glass, the geometry in which it was cooled, and the manner in whichthe glass is crushed (i.e., the crushing technique used), if theparticles were formed by crushing.

Certain articles according to the present invention comprising glass canbe heat- treated to increase or at least partially crystallize the glass(including crystallize the glass) to provide glass-ceramic. Theheat-treatment of certain glasses to form glass-ceramics is well knownin the art. The heating conditions to nucleate and grow glass-ceramicsare known for a variety of glasses. Alternatively, one skilled in theart can determine the appropriate conditions from aTime-Temperature-Transformation (TTT) study of the glass usingtechniques known in the art. One skilled in the art, after reading thedisclosure of the present invention should be able to provide TTT curvesfor glasses according to the present invention, determine theappropriate nucleation and/or crystal growth conditions to providecrystalline ceramics, glass-ceramics, and ceramic comprising glassaccording to the present invention.

Typically, glass-ceramics are stronger than the glasses from which theyare formed. Hence, the strength of the material may be adjusted, forexample, by the degree to which the glass is converted to crystallineceramic phase(s). Alternatively, or in addition, the strength of thematerial may also be affected, for example, by the number of nucleationsites created, which may in turn be used to affect the number, and inturn the size of the crystals of the crystalline phase(s). Foradditional details regarding forming glass-ceramics, see, for exampleGlass-Ceramics, P. W. McMillan, Academic Press, Inc., 2^(nd) edition,1979, the disclosure of which is incorporated herein by reference.

For example, during heat-treatment of a glass such as a glass comprisingAl₂O₃, La₂O₃, and ZrO₂ formation of phases such as La₂Zr₂O₇, and, ifZrO₂ is present, cubic/tetragonal ZrO₂, in some cases monoclinic ZrO₂,have been observed at temperatures above about 900° C. Although notwanting to be bound by theory, it is believed that zirconia-relatedphases are the first phases to nucleate from the glass. For example, ofAl₂O₃, ReAlO₃ (wherein Re is at least one rare earth cation), ReAl₁₁O₁₈,Re₃Al₅O₁₂, Y₃Al₅O₁₂, etc. phases are believed to generally occur attemperatures above about 925° C. Crystallite size during this nucleationstep may be on the order of nanometers. For example, crystals as smallas 10-15 nanometers have been observed. Longer heat-treatingtemperatures typically lead to the growth of crystallites andprogression of crystallization. For at least some embodiments,heat-treatment at about 1300° C. for about 1 hour provides a fullcrystallization.

Certain ceramic articles made according to the present invention containless than less than 20% by weight SiO₂ (or even less than 15%, less than10%, less than, 5% by weight, or even zero percent, by weight, SiO₂),less than 20% by weight B₂O₃ (or even less than 15%, less than 10%, lessthan, 5% by weight, or even zero percent, by weight, B₂O₃), and lessthan 40% by weight P₂O₅ (or even less than 35%, less than 30%, less than25%, less than 20%, less than 15%, less than 10%, less than, 5% byweight, or even zero percent, by weight, P₂O₅), based on the total metaloxide weight of the ceramic.

The microstructure or phase composition (glassy/amorphous/crystalline)of a material can be determined in a number of ways. Various informationcan be obtained using optical microscopy, electron microscopy,differential thermal analysis (DTA), and x-ray diffraction (XRD), forexample.

Using optical microscopy, amorphous material is typically predominantlytransparent due to the lack of light scattering centers such as crystalboundaries, while crystalline material shows a crystalline structure andis opaque due to light scattering effects.

Using DTA, the material is classified as amorphous if the correspondingDTA trace of the material contains an exothermic crystallization event(T_(x)). If the same trace also contains an endothermic event (T_(g)) ata temperature lower than T_(x) it is considered to consist of a glassphase. If the DTA trace of the material contains no such events, it isconsidered to contain crystalline phases.

Differential thermal analysis (DTA) can be conducted using the followingmethod. DTA runs can be made (using an instrument such as that obtainedfrom Netzsch Instruments, Selb, Germany under the trade designation“NETZSCH STA 409 DTA/TGA”) using a—140+170 mesh size fraction (i.e., thefraction collected between 105-micrometer opening size and 90-micrometeropening size screens). An amount of each screened sample (typicallyabout 400 milligrams (mg)) is placed in a 100-microliter Al₂O₃ sampleholder. Each sample is heated in static air at a rate of 10° C./minutefrom room temperature (about 25° C.) to 1100° C.

Using powder x-ray diffraction, XRD, (using an x-ray diffractometer suchas that obtained under the trade designation “PHILLIPS XRG 3100” fromPhillips, Mahwah, N.J., with copper Kα1 radiation of 1.54050 Angstrom)the phases present in a material can be determined by comparing thepeaks present in the XRD trace of the crystallized material to XRDpatterns of crystalline phases provided in JCPDS (Joint Committee onPowder Diffraction Standards) databases, published by InternationalCenter for Diffraction Data. Furthermore, an XRD can be usedqualitatively to determine types of phases. The presence of a broaddiffused intensity peak is taken as an indication of the amorphousnature of a material. The existence of both a broad peak andwell-defined peaks is taken as an indication of existence of crystallinematter within an amorphous matrix. The initially formed amorphousmaterial or ceramic (including glass prior to crystallization) may belarger in size than that desired. The amorphous material or ceramic canbe converted into smaller pieces using crushing and/or comminutingtechniques known in the art, including roll crushing, canary milling,jaw crushing, hammer milling, ball milling, jet milling, impactcrushing, and the like. In some instances, it is desired to have two ormultiple crushing steps. For example, after the ceramic is formed(solidified), it may be in the form of larger than desired. The firstcrushing step may involve crushing these relatively large masses or“chunks” to form smaller pieces. This crushing of these chunks may beaccomplished with a hammer mill, impact crusher or jaw crusher. Thesesmaller pieces may then be subsequently crushed to produce the desiredparticle size distribution. In order to produce the desired particlesize distribution (sometimes referred to as grit size or grade), it maybe necessary to perform multiple crushing steps. In general the crushingconditions are optimized to achieve the desired particle shape(s) andparticle size distribution. Resulting particles that are of the desiredsize may be recrushed if they are too large, or “recycled” and used as araw material for re-melting if they are too small.

The shape of particles can depend, for example, on the compositionand/or microstructure of the ceramic, the geometry in which it wascooled, and the manner in which the ceramic is crushed (i.e., thecrushing technique used). In general, where a “blocky” shape ispreferred, more energy may be employed to achieve this shape.Conversely, where a “sharp” shape is preferred, less energy may beemployed to achieve this shape. The crushing technique may also bechanged to achieve different desired shapes. For some particles anaverage aspect ratio ranging from 1:1 to 5:1 is typically desired, andin some embodiments 1.25:1 to 3:1, or even 1.5:1 to 2.5:1.

Ceramic articles (including glass-ceramics) made according to thepresent invention may comprise at least 1, 2, 3, 5, 10, 15, 20, 25, 30,35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even100 percent by volume crystallites, wherein the crystallites have anaverage size of less than 1 micrometer. In another aspect, ceramicarticles (including glass-ceramics) made according to the presentinvention may comprise less than at least 1, 2, 3, 5, 10, 15, 20, 25,30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, oreven 100 percent by volume crystallites, wherein the crystallites havean average size of less than 0.5 micrometer. In another aspect, ceramics(including glass-ceramics) according to the present invention compriseless than at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55,60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent byvolume crystallites, wherein the crystallites have an average size ofless than 0.3 micrometer. In another aspect, ceramic articles (includingglass-ceramics) made according to the present invention may compriseless than at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55,60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent byvolume crystallites, wherein the crystallites have an average size ofless than 0.15 micrometer. In another aspect, ceramic articles(including glass-ceramics) made according to the present invention maybe free of at least one of eutectic microstructure features (i.e., isfree of colonies and lamellar structure) or a non-cellularmicrostructure.

In another aspect, certain ceramic articles made according to thepresent invention may comprise, for example, at least 1, 2, 3, 5, 10,15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, oreven 100 percent by volume glass. In another aspect, certain ceramicarticles made according to the present invention may comprise, forexample, 100 or at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50,55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent byvolume crystalline ceramic.

Certain articles made according to the present invention comprise glasscomprising CaO and Al₂O₃, wherein at least 80 (85, 90, 95, 97, 98, 99,or even 100) percent by weight of the glass collectively comprises theCaO and Al₂O₃, based on the total weight of the glass.

In another aspect, certain articles made according to the presentinvention provides a ceramic comprising glass (e.g., at least 5, 10, 15,20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98,99, or even 100 percent by volume glass), the glass comprising CaO andAl₂O₃, wherein at least 80 (85, 90, 95, 97, 98, 99, or even 100) percentby weight of the glass collectively comprises the CaO and Al₂O₃, basedon the total weight of the glass.

In another aspect, certain articles made according to the presentinvention provides glass-ceramic comprising CaO and Al₂O₃, wherein atleast 80 (85, 90, 95, 97, 98, 99, or even 100) percent by weight of theglass-ceramic collectively comprises CaO and Al₂O₃, based on the totalweight of the glass-ceramic. The glass-ceramic may comprise, forexample, at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55,60, 65, 70, 75, 80, 85, 90, or 95 percent by volume glass. Theglass-ceramic may comprise, for example, at least 99, 98, 97, 95, 90,85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, or 5percent by volume crystalline ceramic.

In another aspect, certain articles made according to the presentinvention provides a ceramic comprising crystalline ceramic (e.g., atleast 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystalline ceramic), the crystalline ceramic comprising, wherein atleast 80 (85, 90, 95, 97, 98, 99, or even 100) percent by weight of thecrystalline ceramic collectively comprises the CaO and Al₂O₃, based onthe total weight of the crystalline ceramic. The ceramic may comprise,for example, at least 99, 98, 97, 95, 90, 85, 80, 75, 70, 65, 60, 55,50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or 1 percent by volumeglass.

In another aspect, certain articles made according to the presentinvention provides a ceramic comprising crystalline ceramic (e.g., atleast 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystalline ceramic), the ceramic comprising CaO and Al₂O₃, wherein atleast 80 (85, 90, 95, 97, 98, 99, or even 100) percent by weight of theceramic collectively comprises CaO and Al₂O₃, based on the total weightof the ceramic. The ceramic may comprise, for example, at least 99, 98,97, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15,10, 5, 3, 2, or 1 percent by volume glass.

Certain articles made according to the present invention comprise glasscomprising CaO, Al₂O₃, and ZrO₂, wherein at least 80 (85, 90, 95, 97,98, 99, or even 100) percent by weight of the glass collectivelycomprises the CaO, Al₂O₃, and ZrO₂, based on the total weight of theglass.

In another aspect, certain articles made according to the presentinvention provides a ceramic comprising glass (e.g., at least 5, 10, 15,20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98,99, or even 100 percent by volume glass), the glass comprising CaO,Al₂O₃, and ZrO₂, wherein at least 80 (85, 90, 95, 97, 98, 99, or even100) percent by weight of the glass collectively comprises the CaO andAl₂O₃, and ZrO₂, based on the total weight of the glass.

In another aspect, certain articles made according to the presentinvention provides glass-ceramic comprising CaO, Al₂O₃, and ZrO₂,wherein at least 80 (85, 90, 95, 97, 98, 99, or even 100) percent byweight of the glass-ceramic collectively comprises the CaO, Al₂O₃, andZrO₂, based on the total weight of the glass-ceramic. The glass-ceramicmay comprise, for example, at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95 percent by volumeglass. The glass-ceramic may comprise, for example, at least 99, 98, 97,95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10,or 5 percent by volume crystalline ceramic.

In another aspect, certain articles made according to the presentinvention provides a ceramic comprising crystalline ceramic (e.g., atleast 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystalline ceramic), the crystalline ceramic comprising, wherein atleast 80 (85, 90, 95, 97, 98, 99, or even 100) percent by weight of thecrystalline ceramic collectively comprises the CaO, Al₂O₃, and ZrO₂,based on the total weight of the crystalline ceramic. The ceramic maycomprise, for example, at least 99, 98, 97, 95, 90, 85, 80, 75, 70, 65,60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or 1 percent byvolume glass.

In another aspect, certain articles made according to the presentinvention provides a ceramic comprising crystalline ceramic (e.g., atleast 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystalline ceramic), the ceramic comprising CaO, Al₂O₃, and ZrO₂,wherein at least 80 (85, 90, 95, 97, 98, 99, or even 100) percent byweight of the ceramic collectively comprises CaO, Al₂O₃, and ZrO₂, basedon the total weight of the ceramic. The ceramic may comprise, forexample, at least 99, 98, 97, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50,45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or 1 percent by volume glass.

Certain articles made according to the present invention comprise glasscomprising BaO and TiO₂, wherein at least 80 (85, 90, 95, 97, 98, 99, oreven 100) percent by weight of the glass collectively comprises the BaOand TiO₂, based on the total weight of the glass.

In another aspect, certain articles made according to the presentinvention provides a ceramic comprising glass (e.g., at least 5, 10, 15,20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98,99, or even 100 percent by volume glass), the glass comprising BaO andTiO₂, wherein at least 80 (85, 90, 95, 97, 98, 99, or even 100) percentby weight of the glass collectively comprises the BaO and TiO₂, based onthe total weight of the glass.

In another aspect, certain articles made according to the presentinvention provides glass-ceramic comprising BaO and TiO₂, wherein atleast 80 (85, 90, 95, 97, 98, 99, or even 100) percent by weight of theglass-ceramic collectively comprises the BaO and TiO₂, based on thetotal weight of the glass-ceramic. The glass-ceramic may comprise, forexample, at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55,60, 65, 70, 75, 80, 85, 90, or 95 percent by volume glass. Theglass-ceramic may comprise, for example, at least 99, 98, 97, 95, 90,85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, or 5percent by volume crystalline ceramic.

In another aspect, certain articles made according to the presentinvention provides a ceramic comprising crystalline ceramic (e.g., atleast 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystalline ceramic), the crystalline ceramic comprising, wherein atleast 80 (85, 90, 95, 97, 98, 99, or even 100) percent by weight of thecrystalline ceramic collectively comprises the BaO and TiO₂, based onthe total weight of the crystalline ceramic. The ceramic may comprise,for example, at least 99, 98, 97, 95, 90, 85, 80, 75, 70, 65, 60, 55,50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or 1 percent by volumeglass.

In another aspect, certain articles made according to the presentinvention provides a ceramic comprising crystalline ceramic (e.g., atleast 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystalline ceramic), the ceramic comprising BaO and TiO₂, wherein atleast 80 (85, 90, 95, 97, 98, 99, or even 100) percent by weight of theceramic collectively comprises BaO and TiO₂, based on the total weightof the ceramic. The ceramic may comprise, for example, at least 99, 98,97, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15,10, 5, 3, 2, or 1 percent by volume glass.

Certain articles made according to the present invention comprise glasscomprising La₂O₃ and TiO₂, wherein at least 80 (85, 90, 95, 97, 98, 99,or even 100) percent by weight of the glass collectively comprises theLa₂O₃ and TiO₂, based on the total weight of the glass.

In another aspect, certain articles made according to the presentinvention provides a ceramic comprising glass (e.g., at least 5, 10, 15,20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98,99, or even 100 percent by volume glass), the glass comprising La₂O₃ andTiO₂, wherein at least 80 (85, 90, 95, 97, 98, 99, or even 100) percentby weight of the glass collectively comprises the La₂O₃ and TiO₂, basedon the total weight of the glass.

In another aspect, certain articles made according to the presentinvention provides glass-ceramic comprising La₂O₃ and TiO₂, wherein atleast 80 (85, 90, 95, 97, 98, 99, or even 100) percent by weight of theglass-ceramic collectively comprises the La₂O₃ and TiO₂, based on thetotal weight of the glass-ceramic. The glass-ceramic may comprise, forexample, at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55,60, 65, 70, 75, 80, 85, 90, or 95 percent by volume glass. Theglass-ceramic may comprise, for example, at least 99, 98, 97, 95, 90,85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, or 5percent by volume crystalline ceramic.

In another aspect, certain articles made according to the presentinvention provides a ceramic comprising crystalline ceramic (e.g., atleast 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystalline ceramic), the crystalline ceramic comprising, wherein atleast 80 (85, 90, 95, 97, 98, 99, or even 100) percent by weight of thecrystalline ceramic collectively comprises the La₂O₃ and TiO₂, based onthe total weight of the crystalline ceramic. The ceramic may comprise,for example, at least 99, 98, 97, 95, 90, 85, 80, 75, 70, 65, 60, 55,50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or 1 percent by volumeglass.

In another aspect, certain articles made according to the presentinvention provides a ceramic comprising crystalline ceramic (e.g., atleast 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystalline ceramic), the ceramic comprising La₂O₃ and TiO₂, wherein atleast 80 (85, 90, 95, 97, 98, 99, or even 100) percent by weight of theceramic collectively comprises La₂O₃ and TiO₂, based on the total weightof the ceramic. The ceramic may comprise, for example, at least 99, 98,97, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15,10, 5, 3, 2, or 1 percent by volume glass.

Certain articles made according to the present invention comprise glasscomprising REO and Al₂O₃, wherein at least 80 (85, 90, 95, 97, 98, 99,or even 100) percent by weight of the glass collectively comprises theREO and Al₂O₃, based on the total weight of the glass.

In another aspect, certain articles made according to the presentinvention provides a ceramic comprising glass (e.g., at least 5, 10, 15,20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98,99, or even 100 percent by volume glass), the glass comprising REO andAl₂O₃, wherein at least 80 (85, 90, 95, 97, 98, 99, or even 100) percentby weight of the glass collectively comprises the REO and Al₂O₃, basedon the total weight of the glass.

In another aspect, certain articles made according to the presentinvention provides glass-ceramic comprising REO and Al₂O₃, wherein atleast 80 (85, 90, 95, 97, 98, 99, or even 100) percent by weight of theglass-ceramic collectively comprises the REO and Al₂O₃, based on thetotal weight of the glass-ceramic. The glass-ceramic may comprise, forexample, at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55,60, 65, 70, 75, 80, 85, 90, or 95 percent by volume glass. Theglass-ceramic may comprise, for example, at least 99, 98, 97, 95, 90,85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, or 5percent by volume crystalline ceramic.

In another aspect, the present invention provides glass-ceramiccomprising REO and Al₂O₃, wherein, for example, glass-ceramic exhibits amicrostructure comprising crystallites having an average crystallitesize of less than 1 micrometer (typically, less than 500 nanometers,even less than 300, 200, or 150 nanometers; and in some embodiments,less than 100, 75, 50, 25, or 20 nanometers), and (b) is free of atleast one of eutectic microstructure features or a non-cellularmicrostructure. The glass-ceramic may comprise, for example, at least 1,2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85,90, 95, percent by volume glass. The glass-ceramic may comprise, forexample, at least 99, 98, 97, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50,45, 40, 35, 30, 25, 20, 15, 10, or 5 percent by volume crystallineceramic.

In another aspect, certain articles made according to the presentinvention provides a ceramic comprising crystalline ceramic (e.g., atleast 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystalline ceramic), the crystalline ceramic comprising, wherein atleast 80 (85, 90, 95, 97, 98, 99, or even 100) percent by weight of thecrystalline ceramic collectively comprises the REO and Al₂O₃, based onthe total weight of the crystalline ceramic. The ceramic may comprise,for example, at least 99, 98, 97, 95, 90, 85, 80, 75, 70, 65, 60, 55,50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or 1 percent by volumeglass.

In another aspect, certain articles made according to the presentinvention provides a ceramic comprising crystalline ceramic (e.g., atleast 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystalline ceramic), the ceramic comprising REO and Al₂O₃, wherein atleast 80 (85, 90, 95, 97, 98, 99, or even 100) percent by weight of theceramic collectively comprises REO and Al₂O₃, based on the total weightof the ceramic. The ceramic may comprise, for example, at least 99, 98,97, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15,10, 5, 3, 2, or 1 percent by volume glass.

Certain articles made according to the present invention comprise glasscomprising REO and Al₂O₃, wherein at least 80 (85, 90, 95, 97, 98, 99,or even 100) percent by weight of the glass collectively comprises theREO and Al₂O₃, based on the total weight of the glass.

In another aspect, certain articles made according to the presentinvention provides a ceramic comprising glass (e.g., at least 5, 10, 15,20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98,99, or even 100 percent by volume glass), the glass comprising REO,Al₂O₃, and ZrO₂, wherein at least 80 (85, 90, 95, 97, 98, 99, or even100) percent by weight of the glass collectively comprises the REO andAl₂O₃ and ZrO₂, based on the total weight of the glass.

In another aspect, certain articles made according to the presentinvention provides glass-ceramic comprising REO, Al₂O₃, and ZrO₂,wherein at least 80 (85, 90, 95, 97, 98, 99, or even 100) percent byweight of the glass-ceramic collectively comprises the REO and Al₂O₃ andZrO₂, based on the total weight of the glass-ceramic. The glass-ceramicmay comprise, for example, at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95 percent by volumeglass. The glass-ceramic may comprise, for example, at least 99, 98, 97,95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10,or 5 percent by volume crystalline ceramic.

In another aspect, the present invention provides glass-ceramiccomprising REO, Al₂O₃, and ZrO₂, wherein the glass-ceramic (a) exhibitsa microstructure comprising crystallites having an average crystallitesize of less than 1 micrometer (typically, less than 500 nanometers,even less than 300, 200, or 150 nanometers; and in some embodiments,less than 100, 75, 50, 25, or 20 nanometers), and (b) is free of atleast one of eutectic microstructure features or a non-cellularmicrostructure. The glass-ceramic may comprise, for example, at least 1,2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85,90, 95, percent by volume glass. The glass-ceramic may comprise, forexample, at least 99, 98, 97, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50,45, 40, 35, 30, 25, 20, 15, 10, or 5 percent by volume crystallineceramic.

In another aspect, certain articles made according to the presentinvention provides a ceramic comprising crystalline ceramic (e.g., atleast 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystalline ceramic), the crystalline ceramic comprising, wherein atleast 80 (85, 90, 95, 97, 98, 99, or even 100) percent by weight of thecrystalline ceramic collectively comprises the REO, Al₂O₃, and ZrO₂,based on the total weight of the crystalline ceramic. The ceramic maycomprise, for example, at least 99, 98, 97, 95, 90, 85, 80, 75, 70, 65,60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or 1 percent byvolume glass.

In another aspect, certain articles made according to the presentinvention provides a ceramic comprising crystalline ceramic (e.g., atleast 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystalline ceramic), the ceramic comprising REO and Al₂O₃ and ZrO₂,wherein at least 80 (85, 90, 95, 97, 98, 99, or even 100) percent byweight of the ceramic collectively comprises REO, Al₂O₃, and ZrO₂, basedon the total weight of the ceramic. The ceramic may comprise, forexample, at least 99, 98, 97, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50,45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or 1 percent by volume glass.

In another aspect, certain articles made according to the presentinvention provides a ceramic comprising glass (e.g., at least 5, 10, 15,20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98,99, or even 100 percent by volume glass), the glass comprising REO,Al₂O₃, ZrO₂, and SiO₂ wherein at least 80 (85, 90, 95, 97, 98, 99, oreven 100) percent by weight of the glass collectively comprises the REOand Al₂O₃ and ZrO₂, based on the total weight of the glass.

In another aspect, certain articles made according to the presentinvention provides glass-ceramic comprising REO, Al₂O₃, ZrO₂, and SiO₂,wherein at least 80 (85, 90, 95, 97, 98, 99, or even 100) percent byweight of the glass-ceramic collectively comprises the REO and Al₂O₃ andZrO₂, based on the total weight of the glass-ceramic. The glass-ceramicmay comprise, for example, at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95 percent by volumeglass. The glass-ceramic may comprise, for example, at least 99, 98, 97,95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10,or 5 percent by volume crystalline ceramic.

In another aspect, the present invention provides glass-ceramiccomprising REO, Al₂O₃, ZrO₂, and SiO₂, wherein the glass-ceramic (a)exhibits a microstructure comprising crystallites having an averagecrystallite size of less than 1 micrometer (typically, less than 500nanometers, even less than 300, 200, or 150 nanometers; and in someembodiments, less than 100, 75, 50, 25, or 20 nanometers), and (b) isfree of at least one of eutectic microstructure features or anon-cellular microstructure. The glass-ceramic may comprise, forexample, at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55,60, 65, 70, 75, 80, 85, 90, 95, percent by volume glass. Theglass-ceramic may comprise, for example, at least 99, 98, 97, 95, 90,85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, or 5percent by volume crystalline ceramic.

In another aspect, certain articles made according to the presentinvention provides a ceramic comprising crystalline ceramic (e.g., atleast 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystalline ceramic), the crystalline ceramic comprising, wherein atleast 80 (85, 90, 95, 97, 98, 99, or even 100) percent by weight of thecrystalline ceramic collectively comprises the REO, Al₂O₃, ZrO₂, andSiO₂, based on the total weight of the crystalline ceramic. The ceramicmay comprise, for example, at least 99, 98, 97, 95, 90, 85, 80, 75, 70,65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or 1 percent byvolume glass.

In another aspect, certain articles made according to the presentinvention provides a ceramic comprising crystalline ceramic (e.g., atleast 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystalline ceramic), the ceramic comprising REO and Al₂O₃ and ZrO₂,wherein at least 80 (85, 90, 95, 97, 98, 99, or even 100) percent byweight of the ceramic collectively comprises REO, Al₂O₃, ZrO₂, and SiO₂,based on the total weight of the ceramic. The ceramic may comprise, forexample, at least 99, 98, 97, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50,45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or 1 percent by volume glass.

Crystalline phases that may be present in ceramics according to thepresent invention include alumina (e.g., alpha and transition aluminas),BaO, CaO, Cr₂O₃, CoO, Fe₂O₃, GeO₂, HfO₂, Li₂O, MgO, MnO, NiO, Na₂O,P₂O₅, REO, Sc203, SiO₂, SrO, TeO₂, TiO₂, V₂O₃, Y₂O₃, ZnO, ZrO₂, “complexmetal oxides” (including “complex Al₂O₃-metal oxide (e.g., complexAl₂O₃-REO)), and combinations thereof.

Additional details regarding ceramics comprising Al₂O₃, at least one ofREO or Y₂O₃, and at least one of ZrO₂ or HfO₂, including making, using,and properties, can be found in the following disclosures which areincorporated herein by reference: U.S. Ser. Nos. 09/922,527, 09/922,528,and 09/922,530, filed Aug. 2, 2001; U.S. Ser. Nos. 10/211,598,10/211,630, 10/211,639, 10/211,034, 10/211,640, and 10/211,684, filedAug. 2, 2002; and U.S. Pat. No. 7,101,819 and 7,147,544.

Typically, and desirably, the (true) density, sometimes referred to asspecific gravity, of ceramic according to the present invention istypically at least 70% of theoretical density. More desirably, the(true) density of ceramic according to the present invention is at least75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5% or 100% oftheoretical density

Examples of articles according of the present invention includekitchenware (e.g., plates), dental brackets, and reinforcing fibers,cutting tool inserts, abrasive materials, and structural components ofgas engines, (e.g., valves and bearings). Other articles include thosehaving a protective coating of ceramic on the outer surface of a body orother substrate. Further, for example, ceramic according to the presentinvention can be used as a matrix material. For example, ceramicsaccording to the present invention can be used as a binder for ceramicmaterials and the like such as diamond, cubic-BN, Al₂O₃, ZrO₂, Si₃N₄,and SiC. Examples of useful articles comprising such materials includecomposite substrate coatings, cutting tool inserts abrasiveagglomerates, and bonded abrasive articles such as vitrified wheels. Theuse of ceramics according to the present invention can be used asbinders may, for example, increase the modulus, heat resistance, wearresistance, and/or strength of the composite article.

Advantages and embodiments of this invention are further illustrated bythe following examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this invention. All parts andpercentages are by weight unless otherwise indicated. Unless otherwisestated, all examples contained no significant amount of SiO₂, B₂O₃,P₂O₅, GeO₂, TeO₂, As₂O₃, V₂O₅.

EXAMPLE Example 1

A polyethylene bottle was charged with 27.5 grams of alumina particles(obtained under the trade designation “APA-0.5” from Condea Vista,Tucson, Ariz.), 22.5 grams of calcium oxide particles (obtained fromAlfa Aesar, Ward Hill, Mass.) and 90 grams of isopropyl alcohol. About200 grams of zirconia milling media (obtained from Tosoh Ceramics,Division of Bound Brook, N.J., under the trade designation “YTZ”) wereadded to the bottle, and the mixture was milled at 120 revolutions perminute (rpm) for 24 hours. After the milling, the milling media wereremoved and the slurry was poured onto a glass (“PYREX”) pan where itwas dried using a heat-gun. The dried mixture was ground with a mortarand pestle and screened through a 70-mesh screen (212-micrometer openingsize).

After grinding and screening, some of the particles were fed into ahydrogen/oxygen torch flame. The torch used to melt the particles,thereby generating melted glass beads, was a Bethlehem bench burner PM2Dmodel B, obtained from Bethlehem Apparatus Co., Hellertown, Pa.,delivering hydrogen and oxygen at the following rates. For the innerring, the hydrogen flow rate was 8 standard liters per minute (SLPM) andthe oxygen flow rate was 3 SLPM. For the outer ring, the hydrogen flowrate was 23 (SLPM) and the oxygen flow rate was 9.8 SLPM. The dried andsized particles were fed directly into the torch flame, where they weremelted and transported to an inclined stainless steel surface(approximately 51 centimeters (cm) (20 inches) wide with the slope angleof 45 degrees) with cold water running over (approximately 8liters/minute) the surface to form beads.

Examples 2-9

Examples 2-9 glass beads were prepared as described in Example 1, exceptthe raw materials and the amounts of raw materials used are listed inTable 1, below, and the milling of the raw materials was carried out in90 (milliliters) ml of isopropyl alcohol with 200 grams of the zirconiamedia (obtained from Tosoh Ceramics, Division of Bound Brook, N.J.,under the trade designation “YTZ”) at 120 rpm for 24 hours. The sourcesof the raw materials used are listed in Table 2, below. TABLE 1 ExampleWeight percent of components Batch amounts, g 2 CaO: 36 CaO: 18 Al₂O₃:44 Al₂O₃: 22 ZrO₂: 20 ZrO₂: 10 3 La₂O₃: 45 La₂O₃: 22.5 TiO₂: 55 TiO₂:27.5 4 La₂O₃: 36 La₂O₃: 18 TiO₂: 44 TiO₂: 22 ZrO₂: 20 ZrO₂: 10 5 BaO:47.5 BaO: 23.75 TiO₂: 52.5 TiO₂: 26.25 6 La₂O₃: 48 La₂O₃: 24 Al₂O₃: 52Al₂O₃: 26 7 La₂O₃: 40.9 La₂O₃: 20.45 Al₂O₃: 40.98 Al₂O₃: 20.49 ZrO₂:18.12 ZrO₂: 9.06 8 La₂O₃: 43 La₂O₃: 21.5 Al₂O₃: 32 Al₂O₃: 16 ZrO₂: 12ZrO₂: 6 SiO₂: 13 SiO₂: 6.5 9 SrO: 22.95 SrO: 11.47 Al₂O₃: 62.05 Al₂O₃:31.25 ZrO₂: 15 ZrO₂: 7.5

TABLE 2 Raw Material Source Alumina particles (Al₂O₃) Obtained fromCondea Vista, Tucson, AZ under the trade designation “APA-0.5” Calciumoxide particles Obtained from Alfa Aesar, Ward Hill, MA (CaO) Lanthanumoxide particles Obtained from Molycorp Inc., Mountain (La₂O₃) Pass, CASilica particles (SiO₂) Obtained from Alfa Aesar Barium oxide particlesObtained from Aldrich Chemical Co. (BaO) Titanium dioxide particlesObtained from Kemira Inc., Savannah, (TiO₂) GA Strontium oxide particlesObtained from Alfa Aesar (SrO) Yttria-stabilized Obtained from ZirconiaSales, Inc. of zirconium oxide Marietta, GA under the trade designationparticles (Y-PSZ) “HSY-3”

Various properties/characteristics of some of Examples 1-9 materialswere measured as follows. Powder X-ray diffraction (using an X-raydiffractometer (obtained under the trade designation “PHILLIPS XRG 3100”from PHILLIPS, Mahwah, N.J.) with copper K

1 radiation of 1.54050 Angstrom)) was used to qualitatively measurephases present in example materials. The presence of a broad diffusedintensity peak was taken as an indication of the amorphous nature of amaterial. The existence of both a broad peak and well-defined peaks wastaken as an indication of existence of crystalline matter within anamorphous matrix. Phases detected in various examples are reported inTable 3, below. TABLE 3 Phases detected via Hot-pressing Example X-raydiffraction Color T_(g), ° C. T_(x), ° C. temp, ° C. 1 Amorphous* Clear850 987 985 2 Amorphous* Clear 851 977 975 3 Amorphous* Clear 799 875880 4 Amorphous* Clear 821 876 880 5 Amorphous* Clear 724 760 815 6Amorphous* Clear 855 920 970 7 Amorphous* Clear 839 932 965 8 Amorphous*Clear 836 1002 970 9 Amorphous* Clear 875 934 975*glass, as the example has a T_(g)

For differential thermal analysis (DTA), a material was screened toretain glass beads within the 90-125 micrometer size range. DTA runswere made (using an instrument obtained from Netzsch Instruments, Selb,Germany under the trade designation “NETZSCH STA 409 DTA/TGA”). Theamount of each screened sample placed in a 100-microliter Al₂O₃ sampleholder was 400 milligrams. Each sample was heated in static air at arate of 10° C./minute from room temperature (about 25° C.) to 1200° C.

Referring to FIG. 1, line 375 is the plotted DTA data for the Example 1material. Referring to FIG. 1 line 375, the material exhibited anendothermic event at a temperature around 799° C., as evidenced by thedownward curve of line 375. It was believed that this event was due tothe glass transition (T_(g)) of the material. At about 875° C., anexothermic event was observed as evidenced by the sharp peak in line345. It was believed that this event was due to the crystallization(T_(x)) of the material. These T_(g) and T_(x) values for other examplesare reported in Table 3, above.

FIGS. 2-6 are the plotted DTA data for Examples 2, 5, 6, 7, and 9,respectively.

For each of Examples 1-9, about 25 grams of the glass beads were placedin a graphite die and hot-pressed using uniaxial pressing apparatus(obtained under the trade designation “HP-50”, Thermal Technology Inc.,Brea, Calif.). The hot-pressing was carried out in an argon atmosphereand 13.8 megapascals (MPa) (2000 pounds per square inch (2 ksi))pressure. The hot-pressing temperature at which appreciable glass flowoccurred, as indicated by the displacement control unit of the hotpressing equipment described above, are reported for Examples 1-9 inTable 3, above.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention, and it should be understood that thisinvention is not to be unduly limited to the illustrative embodimentsset forth herein.

1. A ceramic comprising: at least two different metal oxides, the atleast two different metal oxides comprising TiO₂ and La₂O₃ or TiO₂ andBaO; less than 20% by weight SiO₂; less than 20% by weight B₂O₃; andless than 40% by weight P₂O₅; the ceramic having a glass transitiontemperature, T_(g), and a crystallization onset temperature, T_(x),andthe difference between T_(g) and T_(x) is at least 5K.
 2. The ceramic ofclaim 1, comprising a glass wherein at least 80% by weight of the glasscollectively comprises the two different metal oxides.
 3. The ceramic ofclaim 1, comprising a glass-ceramic wherein at least 80% by weight ofthe glass-ceramic collectively comprises the two different metal oxides.4. The ceramic of claim 1, comprising less than 10% by weight SiO₂. 5.The ceramic of claim 1, comprising less than 10% by weight B₂O₃.
 6. Theceramic of claim 1, comprising less than 5% by weight P₂O₅.
 7. Theceramic of claim 1, comprising a glass wherein less than 40% by weightof the glass collectively comprises SiO₂, B₂O₃, and P₂O₅.
 8. The ceramicof claim 1, further comprising an additional metal oxide selected fromthe group consisting of Al₂O₃, BaO, CaO, Cr₂O₃, CoO, Fe₂O₃, GeO₂, HfO₂,Li₂O, MgO MnO, NiO, Na₂O, P₂O₅, CeO₂, Dy₂O₃, Er₂O₃, Eu₂O₃, Gd₂O₃, Ho₂O₃,Lu₂O₃, Nd₂O₃, Pr₆O₁₁, Sm₂O₃, Th₄O₇, Tm₂O₃, Yb₂O₃, Sc₂O₃, SiO₂, SrO,TeO₂, TiO₂, V₂O₃, Y₂O₃, ZnO, ZrO₂, and combinations thereof.
 9. Theceramic of claim 8, the additional metal oxide comprising ZrO₂.
 10. Theceramic of claim 1, in a form comprising particles, beads, microspheres,or fibers.
 11. A method of making an article, comprising: providing aglass in a form comprising particles, beads, microspheres, or fibers;the glass comprising: at least two different metal oxides, the at leasttwo different metal oxides comprising TiO₂ and La₂O₃ or TiO₂ and BaO;less than 20% by weight SiO₂; less than 20% by weight B₂O₃; and lessthan 40% by weight P₂O₅; the glass having a glass transitiontemperature, T_(g), and a crystallization onset temperature, T_(x),andthe difference between T_(g) and T_(x) is at least 5K; and heating theglass above the T_(g) to coalesce to form a coalesced shape; and coolingthe coalesced shape.
 12. The method of claim 11, further comprising:providing a substrate including an outer surface; wherein heating theglass above the T_(g) comprises heating the glass such that at least aportion of the glass wets at least a portion of the outer surface; andwherein after cooling, the coalesced shape is attached to the outersurface.
 13. The method of claim 11, wherein at least 80% by weight ofthe glass collectively comprises the two different metal oxides.
 14. Themethod of claim 11, the glass comprising a glass-ceramic wherein atleast 80% by weight of the glass-ceramic collectively comprises the twodifferent metal oxides.
 15. The method of claim 11, the glass comprisingless than 10% by weight SiO₂.
 16. The method of claim 11, the glasscomprising less than 10% by weight B₂O₃.
 17. The method of claim 11, theglass comprising less than 5% by weight P₂O₅.
 18. The method of claim11, the glass collectively comprising less than 40% by weight of SiO₂,B₂O₃, and P₂O₅.
 19. The method of claim 11, the glass further comprisingan additional metal oxide selected from the group consisting of Al₂O₃,BaO, CaO, Cr₂O₃, CoO, Fe₂O₃, GeO₂, HfO₂, Li₂O, MgO, MnO, NiO, Na₂O,P₂O₅, CeO₂, Dy₂O₃, Er₂O₃, Eu₂O₃, Gd₂O₃, Ho₂O₃, LuO₃, Nd₂O₃, Pr₆O₁₁,Sm₂O₃, Th₄O₇, Tm₂O₃, Yb₂O₃, Sc₂O₃, SiO₂, SrO, TeO₂, TiO₂, V₂O₃, Y₂O₃,ZnO, ZrO₂, and combinations thereof.
 20. The method of claim 19, theadditional metal oxide comprising ZrO₂.
 21. The method of claim 11,wherein heating comprises atomizing.
 22. The method of claim 11, whereinthe glass further comprises a second glass having a second glasstransition temperature, T_(g2), and a second crystallization onsettemperature, T_(x2), and the difference between T_(g2) and T_(x2) is atleast 5K.
 23. An article prepared according to the method of claim 11.